Description
Description: Università degli Studi di Milano Bicocca, Dipartimento di Scienze Geologiche e Geotecnologie, Piazza della Scienza 4, I-20126 Milano, Italy. Pyroclastic soils
mantling a wide area of the Campanian Apennines are subjected to recurrent
instability phenomena. This study analyses the 5 and 6 May 1998 event
which affected the Pizzo d’Alvano (Campania, southern Italy). More than
400 slides affecting shallow pyroclastic deposits were triggered by
intense and prolonged but not extreme rainfall. Landslides affected the
pyroclastic deposits that cover the steep calcareous ridges and are soil
slip-debris flows and rapid mudflows. About 30 main channels were deeply
scoured by flows which reached the alluvial fans depositing up to 400 000
m3 of material in the piedmont areas. About 75% of the
landslides are associated with morphological discontinuities such as
limestone cliffs and roads. The sliding surface is located within the
pyroclastic cover, generally at the base of a pumice layer. Geotechnical
characterisation of pyroclastic deposits has been accomplished by
laboratory and in situ tests. Numerical modelling of seepage processes and
stability analyses have been run on four simplified models representing
different settings observed at the source areas. Seepage modelling showed
the formation of pore pressure pulses in pumice layers and the localised
increase of pore pressure in correspondence of stratigraphic
discontinuities as response to the rainfall event registered between 28
April and 5 May. Numerical modelling provided pore pressure values for
stability analyses and pointed out critical conditions where stratigraphic
or morphological discontinuities occur. This study excludes the need of a
groundwater flow from the underlying bedrock toward the pyroclastic cover
for instabilities to occur.